Particle beam devices are used for examining samples (hereinafter also called objects) in order to obtain insights with regard to the properties and behaviour of the samples under specific conditions. One of those particle beam devices is an electron beam device, in particular a scanning electron microscope (also known as SEM) or a transmission electron microscope (also known as TEM).
In the case of an SEM, an electron beam (hereinafter also called primary electron beam) is generated using a beam generator. The electrons of the primary electron beam are accelerated to a predeterminable energy and focused by a beam guiding system, in particular an objective lens, onto a sample to be analyzed (that is to say an object to be analyzed). A high-voltage source having a predeterminable acceleration voltage is used for acceleration purposes. Using a deflection unit, the primary electron beam is guided in a raster-type fashion over a surface of the sample to be analyzed. In this case, the electrons of the primary electron beam interact with the material of the sample to be analyzed. In particular, interaction particles and/or interaction radiation arise(s) as a consequence of the interaction. By way of example, electrons are emitted by the sample to be analyzed (so-called secondary electrons) and electrons of the primary electron beam are backscattered at the sample to be analyzed (so-called backscattered electrons). The secondary electrons and backscattered electrons are detected and used for image generation. An image of the sample to be analyzed is thus obtained.
Furthermore, it is known from the prior art to use combination devices for processing and/or for analyzing a sample, wherein both electrons and ions can be guided onto a sample to be processed and/or to be analyzed. By way of example, it is known for an SEM to be additionally equipped with an ion beam column. Using an ion beam generator arranged in the ion beam column, ions are generated which are used for processing a sample (for example for removing a layer of the sample or for applying material to the sample) or else for imaging. In this case, the SEM serves, in particular, for observing the processing, but also for further analysis of the processed or non-processed sample.
It is desirable to exactly identify, on the surface of the object, the position of the area(s) which is/are to be analyzed or processed. If the position is exactly known, the particle beam of a particle beam device can be guided to this position such that only this area or those areas are analyzed and/or processed. Additionally or alternatively it is known to position the object and, therefore, the area on the surface of the object to be analyzed and/or processed with the best possible precision in the particle beam device such that the particle beam can be guided to the area. It is known to arrange the object on an object holder which is also known as a stage. The object holder is transitionally movable in three directions which are oriented perpendicular to each other. Additionally, the object holder may be rotated around a first rotation axis and/or a second rotation axis, the axes being oriented perpendicular to each other.
For positioning the object holder and, therefore, also the object to be analyzed and/or processed, the object holder is moved in such a way that, for positioning the object to a specific position, the object holder is moved to a specific position which is given by coordinates of a coordinate system. It should be noticed that several coordinate systems in a particle beam device might be relevant for positioning the object, wherein the coordinate systems are related to each other. As a matter of fact, each assembly unit of a particle beam device has its own coordinate system. The object to be analyzed and/or processed also has its own coordinate system.
A specific position on the surface of the object to be analyzed and/or processed has first coordinates in the coordinate system of the object which correspond to second coordinates in the coordinate system of the object holder, wherein the first coordinates and the second coordinates do not have to be identical with respect to their absolute values. For adjusting to a specific position on the surface of the object, it is known to use a coordinate transformation with respect to the above mentioned two coordinate systems and/or further coordinate systems which might be relevant.
When adjusting the object to a specific position by using the object holder, errors might occur. Due to mechanical errors with respect to the object holder or with respect to the movable parts of the object holder and due to the weight of the object on the object holder, movements of the object holder might occur, which do not allow an accurate positioning of the object and/or guiding the particle beam to the object. It may not be possible to determine the values of such errors, for which reason they may be irreproducible. However, they should be considered when positioning the object.
An exposure method for drawing a pattern on a substrate using a charged particle beam device is known. The method includes a detection step of placing a calibration substrate having a plurality of marks on a stage and detecting positions of the plurality of marks by a first position detection section using a charged particle beam and by a second position detection section using light while adjusting a position of the stage, and a correction step of correcting a position where the charged particle beam is incident on the substrate on which the pattern is to be drawn, in accordance with the position of the stage on the basis of the difference between the results detected by the charged particle beam, on one hand, and by the light in the detection step, on the other hand.
It is referred in particular to references US 2009/0039285 A1 and U.S. Pat. No. 6,864,488 B2 as prior art.
A particle beam device providing a particle beam comprising charged particles may be operated using different beam parameters which influence the characteristics of the particle beam. Such beam parameters are, for example, an acceleration voltage influencing a landing energy of the charged particles, the landing energy being the energy which the charged particles have when impinging on the object, a beam current of the particle beam which impinges on the object and voltages of the electrode units used for deflecting and/or shaping the particle beam. Those parameters and further parameters not mentioned here may influence the particle beam.
As mentioned above, an image of a surface of an object may be obtained using a particle beam. The image may be used to identify an area of the surface which is going to be analyzed and/or processed. However, after having identified the area using first beam parameters characterizing a first operation mode of the particle beam device, it might be necessary to change the first beam parameters used for operating the particle beam device into second beam parameters characterizing a second operation mode. The second beam parameters are used to analyze and/or to process the identified area on the object. For example, a lower or higher beam current has to be chosen to achieve a specific effect on the area. Furthermore, the acceleration voltage may be varied to achieve a specific effect. However, it has been discovered that the image characteristics of the particle beam are often changed when varying the beam parameters. In particular, it may happen that a local displacement in the image may occur. In other words, the area on the surface of the object, which has been identified and is to be analyzed and/or processed, cannot be found at coordinates in the second operation mode of the particle beam device which coordinates were identified in the first operation mode of the particle beam device. If this local displacement is not considered, the particle beam of the particle beam device being in the second operation mode may be guided to an area which has not been identified before. Therefore, a wrong area on the surface of the object may be analyzed and/or processed. It may not be possible to determine the values of such local displacements, for which reasons they may be irreproducible. However, they should be taken into consideration.
Therefore, it is desirable to provide a method and a particle beam device for carrying out the method, which method and particle beam device allow for guiding a particle beam device to an identified area on the surface of an object, even if beam parameters of the particle beam device are varied.